Dietary protein-induced changes in excretory function: a general animal design feature

Mammals are ureotelic and respond to an increased protein intake with an increase in glomerular filtration rate and renal plasma flow. Birds and terrestrial insects are uricotelic and following a high protein intake increase tubular urate secretion by the kidney (birds) or Malpighian tubule (insects). Ureogenic fish given NH₄Cl increase gill and renal clearance of urea and gill clearance of ammonia. Renal mass increases in mammals, birds and reptiles given a high protein intake. Thus, animals in general respond to an increase in protein intake with a change in excretory function such as to increase the clearance of the major nitrogenous end-products of protein metabolism. The components of this general animal excretory response include; a redistribution of regional perfusion with increased renal and gill blood flow, increased GFR and gill ammonia clearance, increased renal tubular urate clearance, changes in urea transport protein abundance and/or function and renal hypertrophy. Animal groups differ as to which components are accentuated. Amino acid catabolism with generation of ammonia appears to be a necessary prerequisite for this excretory response to occur. A hypothesis is put forward that ammonia itself is a regulatory molecule and an important signal communicating between amino acid catabolism following an increase in protein intake and the sequence of events leading to a change in excretory function.     

EFFECT OF NITROGEN SOURCE ON PLATYMONAS (CHLOROPHYTA) CELL COMPOSITION AND AMINO ACID UPTAKE RATES1

The effect of nitrogen source (nitrate, ammonia and/or amino acids) on cell composition and amino acid uptake rates was examined. Substantial levels of free amino acids accumulated intracellularly with all nitrogen sources used. Ammonia accumulated only when provided in the medium. The presence of ammonia in the medium decreased the intracellular accumulation of free amino acids, especially arginine. Amino acid uptake rates were suppressed by the presence of excess nitrogen, especially ammonia. However, the suppression of uptake did not show any particular relation to the nitrogenous cell composition.     

Long-term activation of semicarbazide-sensitive amine oxidase lowers circulating levels of uric acid in diabetic conditions

Uric acid is involved in nitrogenous waste in animals, together with ammonia and urea. Uric acid has also antioxidant properties and is a surrogate marker of metabolic syndrome. We observed that the elevated plasma uric acid of high-fat fed mice was normalized by benzylamine treatment. Indeed, benzylamine is the reference substrate of semicarbazide-sensitive amine oxidase (SSAO), an enzyme highly expressed in fat depots and vessels, which generates ammonia when catalysing oxidative deamination. Ammonia interferes with uric acid metabolism/solubility. Our aim was therefore to investigate whether the lowering action of benzylamine on uric acid was related to an improvement of diabetic complications, or was connected with SSAO-dependent ammonia production. First, we observed that benzylamine administration lowered plasma uric acid in diabetic db/db mice while it did not modify uric acid levels in normoglycemic and lean mice. In parallel, benzylamine improved the glycemic control in diabetic but not in normoglycemic mice, while plasma urea remained unaltered. Then, uric acid plasma levels were measured in mice invalidated for AOC3 gene, encoding for SSAO. These mice were unable to oxidize benzylamine but were not diabetic and exhibited unaltered plasma uric levels. Therefore, activated or abolished ammonia production by SSAO was without influence on uric acid in the context of normoglycemia. Our observations confirm that plasma uric acid increases with diabetes and can be normalized when glucose tolerance is improved. They also show that uric acid, a multifunctional metabolite at the crossroads of nitrogen waste and of antioxidant defences, can be influenced by SSAO, in a manner apparently related to changes in glucose homeostasis.     

Nitrogenous excretory materials from the American cockroach

Excreta obtained from both sexes of the American cockroach, Periplaneta americana, maintained on three different diets was examined for the presence of numerous possible nitrogenous materials in an effort to establish what substances are excreted by this insect. It was found that none of the classical terrestrial insect excretory products, including uric acid, could be detected by the methods employed. Rather, ammonia, amino groups, three tryptophan metabolites, unidentified water soluble materials, and water insoluble components constitute most of the total nitrogen excreted. Ammonia seems to be the largest single component, and it was quantitated in fresh and dried excreta. Upon lyophilization of the excreta more than half of the ammonia is lost.     

Ammonia production from amino acids and urea in the caecal contents of the chicken

1. Ammonia production from urea and amino acids in the caecal contents of the chicken was evaluated using 15N-labeled nitrogenous compounds. 2. About 43% of each of urea nitrogen and glutamine amide nitrogen was converted to ammonia nitrogen, but only 25% of epsilon-nitrogen of the added arginine, a precursor of urea, was found in ammonia. 3. Amino nitrogen of the separately added glutamic acid and glycine to be converted to ammonia was 19-20% of their added amounts, whereas that of alpha-alanine was 11%. 4. It is concluded that dietary and urinary amino acids and urea which find their ways into the caeca are useful nitrogen sources for ammonia production by microflora in the caeca of the chicken.     

The Assimilation of Ammonia by Nitrogen-starved Cells of Chlorella vulgaris: Part II. The Assimilation of Ammonia to other Compounds

Ammonia is rapidly assimilated by nitrogen-starved Chlorellacells and converted into soluble organic nitrogenous compounds.During the first 20 minutes of assimilation most of the ammoniawhich has been used can be accounted for as free or combined-amino-nitrogen and amide-nitrogen. Later a smaller proportionof the assimilated ammonia is found in these fractions whileappreciable quantities of basic amino-acids are formed. Theassimilation of ammonia is accompanied by an increase of therates of oxygen absorption and carbon dioxide production; thevalue of the respiratory quotient decreases. Non-reducing sugarand acid-hydrolysable polysaccharide are metabolized rapidly. Possible interpretations of these facts are discussed.     

Glucose alleviates ammonia-induced inhibition of short-chain fatty acid metabolism in rat colonic epithelial cells

Ammonia decreased metabolism by rat colonic epithelial cells of butyrate and acetate to CO2 and ketones but increased oxidation of glucose and glutamine. Ammonia decreased cellular concentrations of oxaloacetate for all substrates evaluated. The extent to which butyrate carbon was oxidized to CO2 after entering the tricarboxylic acid (TCA) cycle was not significantly influenced by ammonia, suggesting there was no major shift toward efflux of carbon from the TCA cycle. Ammonia reduced entry of butyrate carbon into the TCA cycle, and the proportion of CoA esterified with acetate and butyrate correlated positively with the production of CO2 and ketone bodies. Also, ammonia reduced oxidation of propionate but had no effect on oxidation of 3-hydroxybutyrate. Inclusion of glucose, lactate, or glutamine with butyrate and acetate counteracted the ability of ammonia to decrease their oxidation. In rat colonocytes, it appears that ammonia suppresses short-chain fatty acid (SCFA) oxidation by inhibiting a step before or during their activation. This inhibition is alleviated by glucose and other energy-generating compounds. These results suggest that ammonia may only affect SCFA metabolism in vivo when glucose availability is compromised.     

The molecular processes of urea hydrolysis in relation to ammonia emissions from agriculture

Ammonia emissions from the agricultural sector give rise to numerous environmental and societal concerns and represent an economic challenge in crop farming, causing a loss of fertilizer nitrogen. Ammonia emissions from agriculture originate from manure slurry (livestock housing, storage, and fertilization of fields) as well as urea-based mineral fertilizers. Consequently, political attention has been given to ammonia volatilization, and regulations of ammonia emissions have been implemented in several countries. The molecular cause of the emission is the enzyme urease, which catalyzes the hydrolysis of urea to ammonia and carbonic acid. Urease is present in many different organisms, encompassing bacteria, fungi, and plants. In agriculture, microorganisms found in animal fecal matter and soil are responsible for urea hydrolysis. One strategy to reduce ammonia emissions is the application of urease inhibitors as additives to urea-based synthetic fertilizers and manure slurry to block the formation of ammonia. However, treatment of the manure slurry with urease inhibitors is associated with increased livestock production costs and has not yet been commercialized. Thus, development of novel, environmentally friendly and cost-effective technologies for ammonia emission mitigation is important. This mini-review describes the challenges associated with the volatilization of ammonia in agriculture and provides an overview of the molecular processes of urea hydrolysis and ammonia emissions. Different technologies and strategies to reduce ammonia emissions are described with a special focus on the use of urease inhibitors. The mechanisms of action and efficiency of the most important urease inhibitors in relation to agriculture will be briefly discussed.     

Ammonia volatilization from a flooded tropical soil

Summary Ammonia volatilization, which follows upon the application of nitrogenous fertilizers to a flooded tropical soil, was directly measured in the greenhouse and in the field. Most of the ammonia volatilization losses occurred during the first 9 days after nitrogen application. Ammonia volatilization increased markedly with increases in soil pH. Nitrogen losses from ammonium sulfate applied to soils whose pH values were below 7.5 were very small. The losses from urea were much greater than those from ammonium sulfate. Mixing the fertilizer materials with the puddled soil reduced the losses. Ammonia losses from flooded soil were larger than from dry soil, and drying of a flooded soil reduced the duration and magnitude of ammonia volatilization. It is suggested that only a small amount of nitrogen is being lost through ammonia volatilization from many lowland rice soils. re]19750820     

Interorgan ammonia, glutamate, and glutamine trafficking in pigs with acute liver failure

Ammonia reduction is the target for therapy of hepatic encephalopathy, but lack of quantitative data about how the individual organs handle ammonia limits our ability to develop novel therapeutic strategies. The study aims were to evaluate interorgan ammonia metabolism quantitatively in a devascularized pig model of acute liver failure (ALF). Ammonia and amino acid fluxes were measured across the portal drained viscera (PDV), kidneys, hind leg, and lungs in ALF pigs. ALF pigs developed hyperammonemia and increased glutamine levels, whereas glutamate levels were decreased. PDV contributed to the hyperammonemic state mainly through increased shunting and not as a result of increased glutamine breakdown. The kidneys were quantitatively as important as PDV in systemic ammonia release, whereas muscle took up ammonia. Data suggest that the lungs are able to remove ammonia from the circulation during the initial stage of ALF. Our study provides new data supporting the concept of glutamate deficiency in a pig model of ALF. Furthermore, the kidneys are quantitatively as important as PDV in ammonia production, and the muscles play an important role in ammonia removal.     

Ammonia inhibition in anaerobic digestion: A review

Even though ammonia is an essential nutrient for bacterial growth, it may inhibit methanogenesis during anaerobic digestion process if it is available at high concentrations. Therefore, ammonia is regarded as a potential inhibitor during anaerobic digestion, particularly when dealing with complex type of substrates such as manure or the organic fraction of municipal solid waste (OFMSW). Ammonia is produced through biological degradation of nitrogenous matter. Ammonium ion (NH₄⁺) and free ammonia (NH₃) are the two principal forms of inorganic ammonia nitrogen. Both forms can directly and indirectly cause inhibition in an anaerobic digestion system. Particularly, free ammonia (FAN) is a powerful inhibitor in an anaerobic digester above threshold concentrations. Process inhibition is related to the particular characteristics of the substrate to be anaerobically digested, pH, process temperature (mesophilic or thermophilic), type of the seed sludge (inoculum), the reactor configuration and to the concentrations of ammonium and ammonia. In this paper, ammonia inhibition in anaerobic digestion systems and the recovery efforts after inhibition are discussed. Furthermore, the impacts of ammonia inhibition on the microbial population available in anaerobic digesters, namely bacteria and Archaea, are also evaluated in detail.     

Multi-energy metabolic mechanisms of the fungus Fusarium oxysporum in low oxygen environments

The fungus Fusarium oxysporum produces energy under hypoxic and anoxic conditions by denitrification (nitrate respiration) and ammonia fermentation respectively. Here we found that glucose repressed both of these metabolisms, whereas it supported another anoxic metabolism, hetero-lactic acid fermentation. Ammonia fermentation occurred only after the glucose present in the medium was metabolized to ethanol via alcohol fermentation. During this transition, clear diauxic growth was observed. Glucose regulated the activity of the enzymes involved in ammonia fermentation, hetero-lactic acid fermentation, and denitrification. Highest cell growth was supported by hetero-lactic acid fermentation, followed by denitrification and ammonia fermentation. These results indicate that the energy metabolisms of F. oxysporum are dependent not only on environmental O(2) tension but also on the carbon source, and that ammonia fermentation is an adaptative mechanism acting physiologically as a secondary fermentative mechanism replacing the primary hetero-lactic acid fermentation.     

Transient responses of hybridoma cells to lactate and ammonia pulse and step changes in continuous culture

Ammonia and lactate are the major byproducts from mammalian cells grown in medium containing glutamine and glucose. Both can be toxic to cells, and may limit the productivity of commercial bioreactors. The transient and steady-state responses of hybridoma growth and metabolism to lactate and ammonia pulse and step changes in continuous suspension culture have been examined. No inhibition was observed at 40 mM lactate. Cell growth was inhibited by 5 mM ammonia, but the cells were able to adapt to ammonia concentrations as high as 8.2 mM. Ammonia production decreased and alanine production increased in response to higher ammonia concentrations. Increased ammonia concentrations also inhibited glutamine and oxygen consumption. The specific oxygen consumption rate decreased by an order of magnitude after an ammonia pulse to 18 mM. Under these conditions, over 90% of the estimated ATP production was due to glycolysis and a large fraction of glutamine was converted to lactate.     

Metabolism of urea in Chlorella ellipsoidea

The effect of cyanide on ammonia and urea metabolism was studiedwith intact cells of Chlorella ellipsoidea Gerneck, a greenalga which apparently lacks urease. Ammonia uptake was inhibited more readily by cyanide than wasurea uptake. Urea uptake was stimulated by lower concentrationsof cyanide. The addition of cyanide caused the formation ofammonia from some cellular nitrogenous compounds. In the presenceof exogenously added urea, the molar ratio of ammonia accumulatedin the medium to urea taken up exceeded 2.0 as the cyanide concentrationincreased. However, the molar ratio of ammonia actually producedfrom urea nitrogen to urea taken up was less than 1.35 at anyconcentration of cyanide tested. In the presence of higher concentrationsof cyanide, the rate of incorporation of ¹⁵N into amino acidsfrom ¹⁵N-urea was higher than that from ¹⁵N-ammonium sulfate. The results suggest that Chlorella ellipsoidea possesses a pathwaythrough which urea nitrogen is assimilated directly withouta preliminary breakdown to ammonia. (Received October 18, 1976; )     

Nitrogen excretion by the sheep abomasal parasite Teladorsagia circumcincta

Excretion of nitrogenous substances by Teladorsagia circumcincta was investigated during incubation of L3 in phosphate buffer for up to 30 h and adult worms for 4-6 h. Ammonia was the main excretory product, with about 20% urea. For the first 4-6 h, ammonia excretion by L3 was temperature dependent, directly proportional to the number of larvae, but independent of the pH or strength of the phosphate buffer. Later, ammonia excretion slowed markedly in L3 and adults and reversed to net uptake in L3 by 30 h. An initial external ammonia concentration of 600 μM did not alter the pattern or magnitude of excretion. Re-uptake of ammonia did not occur at extremes of pH or low buffer strength and was slightly reduced at the highest external concentrations. Ammonium transporters and enzymes of glutamate metabolism, including glutamate dehydrogenase, glutamine synthetase and possibly glutamate synthase, are worthy of further investigation as anthelmintic targets.     

Studies on the Metabolism of Aspergilli

Studies were made on the endogenous respiration of Aspergillus sojae K.S. Observing the changes of Kjeldahl-nitrogen in each fraction of the mycelial components, the author concluded that pool amino acids, bound amino acids, protein, nucleic acids and nucleotides covered whole of the nitrogenous reserves available for endogenous respiration in the mycelia. A study was carried out on the effect of preincubation with glucose or amino acids on endogenous respiration. Stimulation of either oxygen uptake, protein breakdown or ammonia formation was observed during respiration of the mycelia incubated with a suitable concentration of azide, 2,4-dinitrophenol, potossium fluoride, monoiodoacetic acid or ethylenediaminetetraacetic acid. Ammonia formation accompanied with endogenous respiration seemed to proceed inversely by the influence of energy yielding reaction.     

The urea cycle and related pathways in the liver of Walker-256 tumor-bearing rats

The urea cycle was evaluated in perfused livers isolated from cachectic tumor-bearing rats (Walker-256 tumor). Urea production in livers of tumor-bearing rats was decreased in the presence of the following substrates: alanine, alanine + ornithine, alanine + aspartate, ammonia, ammonia + lactate, ammonia + pyruvate and glutamine. Urea production from arginine was higher in livers of tumor-bearing rats. No difference was found with aspartate, aspartate + ammonia, citrulline, citrulline + aspartate and glutamine + aspartate. Ammonia consumption was smaller in livers from cachectic rats when the substance was infused together with lactate and pyruvate. Glucose production was smaller in the cachectic condition only when alanine was the gluconeogenic substrate. Blood urea was higher in tumor-bearing rats, suggesting higher rates of urea production. The availability of aspartate seems to be critical for urea synthesis in the liver of tumor-bearing rats, which is possibly unable to produce this amino acid in sufficient amounts from endogenous sources. The liver of tumor-bearing rats may have a different exogenous substrate supply of nitrogenous compounds. Arginine could be one of these compounds in addition to aspartate which seems to be essential for an efficient ureogenesis in tumor-bearing rats.     

Resveratrol Prevents Ammonia Toxicity in Astroglial Cells

Ammonia is implicated as a neurotoxin in brain metabolic disorders associated with hyperammonemia. Acute ammonia toxicity can be mediated by an excitotoxic mechanism, oxidative stress and nitric oxide (NO) production. Astrocytes interact with neurons, providing metabolic support and protecting against oxidative stress and excitotoxicity. Astrocytes also convert excess ammonia and glutamate into glutamine via glutamine synthetase (GS). Resveratrol, a polyphenol found in grapes and red wines, exhibits antioxidant and anti-inflammatory properties and modulates glial functions, such as glutamate metabolism. We investigated the effect of resveratrol on the production of reactive oxygen species (ROS), GS activity, S100B secretion, TNF-α, IL-1β and IL-6 levels in astroglial cells exposed to ammonia. Ammonia induced oxidative stress, decreased GS activity and increased cytokines release, probably by a mechanism dependent on protein kinase A (PKA) and extracellular signal-regulated kinase (ERK) pathways. Resveratrol prevented ammonia toxicity by modulating oxidative stress, glial and inflammatory responses. The ERK and nuclear factor-κB (NF-κB) are involved in the protective effect of resveratrol on cytokines proinflammatory release. In contrast, other antioxidants (e.g., ascorbic acid and trolox) were not effective against hyperammonemia. Thus, resveratrol could be used to protect against ammonia-induced neurotoxicity.     

Synergism between ammonia, lactic acid and carboxylic acids as kairomones in the host-seeking behaviour of the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae)

Host odours play a major role in the orientation and host location of blood-feeding mosquitoes. Anopheles gambiae Giles sensu stricto, which is the most important malaria vector in Africa, is a highly anthropophilic mosquito species, and the host-seeking behaviour of the females of this mosquito is guided by volatiles of human origin. Ammonia, lactic acid and several carboxylic acids are known to be present in the human odour blend. We investigated the effect of these compounds on naive female mosquitoes using a dual-port olfactometer. Ammonia was an attractant on its own, whereas lactic acid was not attractive. Carboxylic acids, offered as a mixture of 12 compounds, were repellent at the concentration tested. The addition of ammonia to the carboxylic acid mixture overruled the repellent effect of the latter. Combining ammonia with either lactic acid or the carboxylic acids did not enhance the attractiveness of ammonia alone. However, a synergistic effect was found when ammonia, lactic acid and the carboxylic acids were applied as a blend. Our findings indicate that An. gambiae s.s. relies on the combination of ammonia, lactic acid and carboxylic acids in its orientation to human hosts. The role of lactic acid in this tripartite synergism differs from that reported for the yellow fever mosquito Aedes aegypti.     

Studies in the Physiology of Lichens: With two Figures in the Text: The Effects of Starvation and of Ammonia Absorption upon the Nitrogen Content of Peltigera polydactyla

Discs cut from the thallus of the lichen Peltigera polydactylacontain relatively large amounts of ammonia nitrogen and smallamounts of amide nitrogen. During starvation in the dark theamounts of ammonia and amide nitrogen remain unchanged, butthe amount of amino-nitrogen increases. Absorption of ammoniaresults in increases in the amounts of ammonia and amino-nitrogenin the discs, but not in the amount of amide nitrogen. It istherefore concluded that amides do not have an important quantitativerole in the nitrogen metabolism of the discs. Ammonia absorption is stimulated by addition of glucose to themedium, but the very slow rate of protein synthesis is onlyslightly increased by glucose. The rate of nitrate absorptionis much slower than that of ammonia absorption. The ecological implications of the results are discussed, andexisting knowledge of the nitrogen metabolism of lichens isreviewed.